Variable flowpath casings for blade tip clearance control

Abstract

Disclosed herein are example variable flowpath casings for blade tip clearance control. An example casing for a turbine engine includes an annular substrate extending along an axial direction, the annular substrate including a first surface and a second surface that is radially inward relative to the first surface; an actuator structure coupled to the second surface of the annular substrate; and a smart structure cantilevered from the second surface of the annular substrate, the smart structure including: a support structure, a first region of the support structure coupled to the second surface of the annular substrate, a second region of the support structure coupled to the actuator structure; and a radially inward surface defining a variable surface, the support structure to move the variable surface in a radial direction.

What is claimed is: 
     
         1 . An apparatus comprising:
 a shroud having a first radial surface located adjacent to a casing, the shroud including a first material associated with a first coefficient of thermal expansion; and   an actuation system to couple the shroud to the casing, the actuation system including:
 a lever arm coupled to the shroud via a first hinge joint; 
 an outer radial linkage having a first end and a second end, the first end coupled to the casing, the second end coupled to the lever arm via a second hinge joint, the outer radial linkage including a second material associated with a second coefficient of thermal expansion that is larger than the first coefficient of thermal expansion; and 
 an inner radial linkage having a third end and a fourth end, the third end coupled to the casing, the fourth end coupled to the lever arm via a third hinge joint, the inner radial linkage disposed between the shroud and the outer radial linkage such that the inner radial linkage is closer to the outer radial linkage than to the shroud. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the outer radial linkage has a first radial length based on a first temperature of ambient air that surrounds the actuation system, the outer radial linkage has a second radial length based on a second temperature of the ambient air, the second temperature higher than the first temperature, and the first radial length is larger than the second radial length. 
     
     
         3 . The apparatus of  claim 2 , wherein the inner radial linkage includes a third material having a third coefficient of thermal expansion that is negative. 
     
     
         4 . The apparatus of  claim 3 , wherein the inner radial linkage has a third radial length based on the first temperature of the ambient air, the outer radial linkage has a fourth radial length based on the second temperature of the ambient air, and wherein the third radial length is smaller than the fourth radial length. 
     
     
         5 . The apparatus of  claim 4 , wherein the first radial surface of the shroud is located at a first radial distance from the casing when the ambient air has the first temperature, and wherein the first radial distance is based on the first radial length of the outer radial linkage and the third radial length of the inner radial linkage. 
     
     
         6 . The apparatus of  claim 5 , wherein the first radial surface of the shroud is located at a second radial distance from the casing when the ambient air has the second temperature, the second radial distance based on the second radial length of the outer radial linkage and the fourth radial length of the inner radial linkage, and wherein the first radial distance is smaller than the second radial distance. 
     
     
         7 . The apparatus of  claim 1 , wherein the shroud includes a second radial surface opposite the first radial surface, the shroud including at least one of a cover or an abradable material coupled to the second radial surface. 
     
     
         8 . A variable flowpath system comprising:
 a casing having a first surface; and   a shroud having a second surface facing the first surface of the casing, the shroud coupled to the casing via a hinge set, the hinge set including:
 a lever arm having (a) a first pin joint, (b) a second pin joint, and (c) a third pin joint disposed between the first pin joint and the second pin joint, the shroud coupled to the first pin joint; 
 a first radial arm coupled between the casing and the second pin joint, wherein the first radial arm is associated with a first coefficient of thermal expansion that is larger than a second coefficient of thermal expansion associated with the shroud; and 
 a second radial arm coupled between the casing and the third pin joint. 
   
     
     
         9 . The variable flowpath system of  claim 8 , wherein a first axial distance is defined between the first pin joint and the third pin joint, a second axial distance is defined between the third pin joint and the second pin joint, a lever ratio is defined based on a ratio of the first axial distance to the second axial distance, and wherein the lever ratio is greater than 1. 
     
     
         10 . The variable flowpath system of  claim 9 , wherein the first radial arm has a first radial length based on a first ambient temperature, the first radial arm has a second radial length based on a second ambient temperature, and wherein a difference between the first radial length and the second radial length is based on the first coefficient of thermal expansion, one of the first radial length or the second radial length, the lever ratio, and a difference between the first ambient temperature and the second ambient temperature. 
     
     
         11 . The variable flowpath system of  claim 8 , wherein the hinge set is a first hinge set coupled to a first circumferential edge of the shroud, and wherein the variable flowpath system further includes a second set hinge set coupled to a second circumferential edge of the shroud. 
     
     
         12 . The variable flowpath system of  claim 11 , further including a third set hinge set coupled to the first circumferential edge of the shroud and a fourth set hinge set coupled to the second circumferential edge of the shroud. 
     
     
         13 . The variable flowpath system of  claim 12 , further including:
 a first guide structure extending radially inward from the first surface of the casing to the first circumferential edge of the shroud; and   a second guide structure extending radially inward from the first surface of the casing to the second circumferential edge of the shroud, wherein the first and second guide structures axially restrain the shroud.   
     
     
         14 . The variable flowpath system of  claim 8 , wherein the casing includes a honeycomb structure coupled to the first surface. 
     
     
         15 . The variable flowpath system of  claim 8 , wherein the shroud is a first shroud coupled to the casing via a first hinge set, and further including a second shroud coupled to the casing via a second hinge set, wherein the second shroud is located circumferentially adjacent to the first shroud. 
     
     
         16 . The variable flowpath system of  claim 8 , wherein a radial distance between the second surface of the shroud and the first surface of the casing is based on respective radial lengths of the first and second radial arms. 
     
     
         17 . A turbine engine defining an axial direction, a radially direction, and a circumferential direction, the turbine engine comprising:
 a casing; and   a variable flowpath system coupled to the casing, the variable flowpath system including:
 a shroud segment located radially inward from the casing, the shroud segment rotatably coupled to a first end of a lever; 
 a first arm extending radially inward from the casing, the first arm rotatably coupled to a second end of the lever, wherein the first arm is associated with a first coefficient of thermal expansion such that the first arm has a first length based on a first ambient temperature and a second length based on a second ambient temperature; and 
 a second arm extending radially inward from the casing adjacent to the first arm, wherein the second arm is rotatably coupled to the lever at a location between the first end of the lever and the second end of the lever. 
   
     
     
         18 . The turbine engine of  claim 17 , wherein the shroud segment is located radially adjacent to a rotor blade, wherein a distance is defined between the shroud segment and a tip of the rotor blade, and wherein the distance is at least 20 mils and less than 40 mils. 
     
     
         19 . The turbine engine of  claim 17 , wherein the shroud segment is spaced apart from the casing to define a gap therebetween, wherein a dimension of the gap is based at least partially on whether the first arm has the first length or the second length. 
     
     
         20 . The turbine engine of  claim 17 , further including a damper, wherein the damper is coupled to a radial inner surface of the casing such that the damper is located radially between the casing and the shroud segment.